1. Field of Invention
This invention relates to a device for reducing the erosion caused at point in process equipment where the pressure of a flowing liquid containing abrasive solids is reduced. More particularly, the invention relates to a pressure let-down assembly useful in the handling of liquefied coal.
2. Description of the Prior Art
Processing equipment used for the handling of high pressure liquids containing abrasive solids, such as liquids containing ash particles produced from the liquefication of coal, is subjected to severe erosion. As a result, frequent shutdowns are required to replace eroded parts. This erosion problem is particularly acute in pressure let-down valves since these valves reduce fluid pressures from about 1,000 to 3,000 psi to pressures close to atmospheric. This rapid pressure reduction results in fluid velocities ranging from near sonic to supersonic. Because of these high fluid flow rates, erosion of the process equipment is so rapid that replacement of valves and other associated parts may be required within a few hours or days. The erosion of the valve body can at least be partially eliminated by coating the valve with hard abrasive resistant materials, such as tungsten carbide. However, this solution is not totally satisfactory because of the uneven erosion rates in the valve. Moreover, merely coating the valve does not reduce erosion in the pipes which are downstream from the valve and which are also subjected to high fluid velocities. This erosion can be eliminated by providing an impingement plug, coated with a hard abrasion-resistant material such as tungsten carbide, in flow alignment with the fluids exiting from the valve. This plug absorbs much of the energy of the fluids and changes its flow direction.